1. Field of the Invention
The present invention relatest to a fault tolerant network arrangement using a dual cross path for real-time switching and packet handling method.
2. Discussion of Related Art
When a fault occurs in a communication network, a dual ring, or forward-direction and reverse-direction cross paths is conventionally used to enable communication to perform. However, with the dual ring, switching time becomes longer as the number of node composing the ring increases because the switching time depends on the number of node. Furthermore, time for detecting the fault is required. Moreover, in case of conventional forward-direction and reverse-direction cross paths, though there are many substitute paths for preparing occurrence of a fault, the algorithm is complicated. This does not allow the actual application.
FIG. 1 is a view showing an arrangement of a conventional dual fiber distributed data interface (referred to hereinafter as FDDI) network under a normal condition and FIG. 2 is a view showing an arrangement of the conventional dual FDDI network upon occurrence of a fault. The conventional dual FDDI network is constructed in such a manner that nodes 10, 20, 30 and 40 are connected to one another through a dual ring. Referring to FIG. 2, upon the occurrence of the fault at nodes 30 and 40 among nodes 10, 20, 30 and 40 connected through the dual network, the remaining nodes 10 and 20 are rearranged through a single network so that they can normally communicate with each other.
Namely, under the normal condition, the communications are performed in the opposite directions through the two lines as shown in FIG. 1. If the fault occurs at a certain node or link, the remaining nodes are rearranged through the single network as shown in FIG. 2. As a result, the normal nodes can communicate with each other. In this manner, the conventional dual FDDI network must first detect the fault to process it. With the fault detected, the remaining nodes are rearranged through the single line, for message transmission and reception. However, the above-mentioned conventional dual FDDI network with the dual line has disadvantages in that the fault detection must be carried out in real-time, and time required for the rearrangement depends on the number of nodes constituting the network.
FIG. 3 shows a structure of a conventional dual cross paths in DRDT network. Referring to FIG. 3, the packets of two DRDT interface units 50 and 60 pass through each link, and one packet reaches to the final destination in a manner that four packets are transmitted through four paths to the nodes. With this structure, the real-time fault detection is not required because the fault is detected according to the network structure, contrast to the aforementioned method in which the fault is first detected, and then processed.
Each node composing the ring in DRDT network is composed of two DRDT nodes (referred to hereinafter as D-node). If fault occurs in both of the two nodes simultaneously, an island is made in the interconnection network. However, if only one D-node fault at each ring node, DRDT performs normal operation. When the fault occurs at both upper-level D-node composing ring node (referred to hereinafter as D-node/U) and lower-level D-node composing ring node (D-node/L) simultaneously, it is mostly due to power failure or maintenance problem.
FIG. 3 shows how the packets are passing DRDT network for the given DRDT configuration. In this configuration, D-node/Us 71, 72, 73 and 74 locationally correspond to D-node/Ls 81, 82, 83 and 84. The packet transmitted from DRDT interface unit (DIFU) 50 is duplicated by a passive splitter to be passed to D-nodes 71 and 81. The packet stored in the queue of first DIFU 50 is duplicated and passed from first D-node/U 71 to second D-nodes 72 ad 82, and the D-node/L 81 passes the packet to second D-nodes 72 and 82 in the same way. The packet duplication is performed by a passive splitter as in DIFUs 50 and 60. Second D-node/U 72 and second D-node/L 82 choose one of the redundant received packets and pass the selected packet to the next stage through a passive splitter. In the fourth D-nodes 74 and 84, the fourth D-node/U 74 and fourth D-node/L 84 choose one of the duplicated packets respectively, recognize that it is the final node, and pass the packet to DIFU through the queue. DIFU finally chooses one of the received duplicated packets from fourth D-node/U 74 and fourth D-node/L 84.
As explained above, the packets are duplicated and selected link by link, which allows only a single same packet at each link, i.e. for a packet to arrive its final destination, four packets are passed from each D-node to D-node using four paths.
FIG. 4 is a conventional D-node block diagram, showing the structure of the D-node for DRDT network of FIG. 3.
Referring to FIG. 4, D-node is composed of two interface units, packet processing module (PHM) 93, fault detection handling module (FDHM) 94, and lookup table 95. FIG. 5 shows a conventional DIFU configuration. Referring to FIG. 5, DIFU is constructed in a manner that PHM 130, FDHM 140, lookup table 150 and processor 160 are connected. DIFU of FIG. 5 is used for connection to the host.